Ultrasound Examination of the Anal Sphincter - HD

Introduction

Hello, my name is Leslie Scott.
I'm a professor of radiology
and surgery at Yale University School of Medicine,
where I am vice chair for education
and associate program director in the department
of Radiology and Biomedical Imaging.
And today we're gonna talk about ultrasound evaluation
of the a**l sphincter.
And I have no disclosures that are relevant
to this particular presentation.

Objectives

And my objectives are to discuss first the technique
and normal anatomy of the a**l sphincter.
And then I'm gonna concentrate on talking about,
ultrasound evaluation of tears of the a**l sphincter.
At the end of the lecture, we'll briefly talk about the role
of ultrasound and evaluating patients with per rectal
or perianal abscesses and fistula.
And then at the very end, briefly discuss the potential
of ultrasound to stage patients with rectal cancer.

Fecal Incontinence and Causes

So patients usually present to us for evaluation
of the a**l sphincter because of fecal incontinence.
And fecal incontinence is approximately six
to eight times more common in women than in men.
And it's estimated in the United States that somewhere
between one and 15% of all women over the age
of 64 years have some degree of fecal incontinence.
And it is my opinion,
and I hope to convince you today
that ultrasound should be considered the first line imaging
modality of choice to evaluate sphincter integrity.
And what your goal really is when you do this, is
to differentiate a tear in the sphincter versus neurogenic
causes of fecal incontinence,
in which case the sphincter will be intact.
It's also important to determine the extent of the tear
and whether or not the sphincter is actually fragmented
because that will affect management.
And occasionally you will see atrophy of the phi sphincter
as a cause of fecal incontinence.

Now the vast majority of patients
with fecal incontinence actually do have a tear
of the a**l sphincter.
And by far
and away the most common cause
of such tears is obstetrical trauma.
So this is much more common in women who have had children
and tears are particularly common if there has been
mechanical disruption of the sphincter during delivery
because of a, a midline app, episiotomy use of forceps
or a large baby.
But occasionally,
traction injury
during birth can actually tear the nerves leading to,
rectal or sphincter incontinence,
although the sphincter is anatomically intact.
Other causes of direct injury
to the sphincter would include trauma
or, a**l rectal surgery.
However, there are several things
that will cause finkel incontinence in the presence
of an intact sphincter.
And these include diabetes.
Other neurogenic causes certain medications advancing age in
patients who are treated with radiation therapy.

Anatomy of the Anal Sphincter

There are two basic components to the,
sphincter complex, the internal
and the external a**l sphincter.
The internal a**l sphincter is an involuntary smooth muscle
and this provides about 85% of resting a**l tone.
And it is derived as a condensation
of the circular inner smooth muscle
of the muscularis propria in the rectal wall.
And it runs from the a**l rectal junction
to approximately one centimeter above the a**l verge.
It tends to be thickest in the mid portion.
It's usually similar in thickness in men as in women,
and it averages about two
to four millimeters in maximal dimension.
And the thickness of the internal a**l sphincter tends
to increase with age.

The outer component of the sphincteric complex,
namely the external sphincter,
is comprised of smooth muscle.
And this does not begin as far as cephalad,
at least anteriorly as the internal a**l sphincter.
And in the cephalad portion it is typically fused
or very closely related
to the puborectalis muscle posteriorly.
It extends however lower than the internal a**l sphincter
to the,
opening of the,
a**l orifice
and at least a centimeter below the lower margin
of the internal a**l sphincter.
And the diameter of the external a**l sphincter tends
to decrease with age.

Here is a schematic,
anatomic drawing
and you can see the a**l canal,
centrally outside it.
You see this hypo coic band
and this is a, a coronal plane
and this is the internal sphincter.
Outside of that, you'll see a band which is more echogenic
on ultrasound, which is the external sphincter.
And in between you sometimes see these wisps
of longitudinal fibers, a longitudinal layer of muscle
that's in the inter sphincteric space

on a three-dimensional ultrasound, you can see
that the internal sphincter is typically,
in the,
very, very hypo coic, almost black.
And again in the coronal plane you can see
that it parallels the wall of the a**l canal.
And outside of that more peripheral will be the
echogenic external sphincter.
And as you can see, it extends,
further south,
if you will, than the bottom of the internal sphincter.
And here you can see a,
further depiction showing
that the external sphincter extends a little bit more
inferiorly than the internal a**l sphincter.

Ultrasound Technique

Now we evaluate in our laboratory the sphincter complex
using transrectal ultrasound,
and we do this with a rotating
or scifi probe that's at least seven
to 10 megahertz in frequency.
And we generally examine our patients in the left lateral
decubitus position with the knees bent.
And the probe of course is covered with a condom
and is lubricated extensively.
And it's sometimes helped to have a lubricant
that has a little bit of lidocaine within it in case
it's a little bit painful.

Now no patient preparation is required,
for doing this exam,
but I always do proceed the examination
with a digital rectal exam in order to assess rectal tone.
And I will ask the patient to squeeze around my finger so
that I can determine if they can squeeze
adequately circumferentially
or if in the presence of the more most common,
rectal tear that's located anteriorly.
Often you can feel that they can com squeeze
and clench the rectum posteriorly, but there is no movement
or clenching palpable anteriorly.

I then insert the probe
and I start superiorly
to identify the striated rectal gut wall signature.
And when I see this striated gut wall signature,
I know I'm in the rectum and I'm up above the sphincter.
I then pull out very slowly
to identify the pubal recile muscle.
And after that I continue
to slowly pull out the probe imaging every few centimeters,
making sure to image in the high portion, the mid portion
and the lower portion.
And if I have any questions, I will repeat that,
having the patient clench
because the clenching maneuver often helps define the
margins of a sphincter tear.

Normal Anatomy on Ultrasound

So starting with the normal anatomy, you can see
that we've put in the probe high up above the sphincter
and you can recognize the clear striations
of the normal rectal wall where you see these rings
of echogenic material surrounded by a ring
of hypo coke material, another echogenic ring,
a hypo coke ring,
and then an outer echogenic ring
representing the peri rectal fat.
And when you identify this, you know you are in the rectum,
you're up above the a**l sphincter complex
and this is a landmark I use to know
that I've inserted the probe high enough
and then I slowly start to pull it out.

The first thing that you will see as you pull out
and you lose that striated appearance
of the rectal wall will be the pubal recal muscle.
And this is a u
or horseshoe shaped,
structure that's usually
of intermediate to echogenicity to slightly echogenic.
And you can see that it has again, these parallel blands
and it really is a sling that you can,
see in this transverse plane that's just holding the rectum,
and a**l canal in place.
And this marks the superior portion
of the internal sphincter, which you begin to see
as this very hypo colic ring around the probe.

This is,
a picture of the normal anatomy
of the a**l sphincter.
And you can see centrally this is the probe here,
surrounded by a fluid
and the echogenic material around that is the
mucosa and submucosa.
And then you see this hypo coic 360 degree ring,
sometimes very, very hypo coic, almost anti coic.
And this is the typical appearance
of the internal a**l sphincter.
Outside of that, in the transverse plane, you're going
to see a 360 degree ring in the mid
to lower a**l canal,
which represents the external sphincter.
And you can sometimes see these little parallel
bands,
within it.
And as I said, it should go 360 degrees
around the internal a**l sphincter

between the two sphincters.
You sometimes see these hypoechoic wispy little rings.
Rarely are these confluent 360 degrees.
You just sort of see this in pieces.
And these represent these longitudinal muscle fibers in the
inter sphincteric space.

I would like to point out
that there is some variability in the echogenicity
of the external sphincter
and sometimes it can be a little bit more hypo coic than
this, but in general, it is substantially more echogenic
than the internal sphincter.

Now we talk about the sphincter,
in relation to the face
of the clock with 12 o'clock being anteriorly, six o'clock
by the cocc, six being posteriorly,
three o'clock the patient's left
and nine o'clock is the patient's right.
And so once again, you can see here the probe centrally
surrounded by the echogenic mucosa
and some mucosa, the very hypo coic 360 degrees
intact, normal internal sphincter.
And then the more echogenic surrounding
external sphincter in again a normal patient.

So just to review the landmarks that I use,
I know I'm in the upper portion if I'm just inferior to
that horseshoe shaped echogenic sling
of the pubal erectile muscle.
And remember that when you're in the upper portion
of the a**l canal,
you will not identify the external a**l sphincter
anteriorly in the mid portion.
This is where the internal a**l sphincter
is going to be thickest.
And you are going to see a complete external
a**l sphincter ring in the normal patient
and lower down in the a**l canal.
The internal a**l sphincter will not be present,
but remember that the external a**l sphincter will extend at
least a centimeter coddle to the end
of the internal a**l sphincter in the normal patient.

Ultrasound Evaluation of Sphincter Tears

And tears are very easily detected on ultrasound
as discontinuity of the structures that I've just described.
So here is a patient that has a very large tear anteriorly,
of both the internal and the a**l sphincter.
And we would describe this again in terms
of the face of the clock.
And you can see this big hypo coic tear disrupting the
echogenic,
echo texture of the external sphincter
and extends approximately from 11 o'clock
to the three o'clock position.
Underneath you can see the internal sphincter
and you can see that it's attenuated from about one o'clock
to three o'clock, but it's clearly disrupted from about one
o'clock to the 11 or 1130,
o'clock position.

Here's another example of a patient
with a large anterior tear,
which again extends from approximately,
11 o'clock to three o'clock.
And here on another image, 11 o'clock
to three o'clock in the external sphincter.
And here the internal sphincter, it extends from 12 o'clock
to three o'clock where you see complete disruption
of the hypoechoic,
ring of the internal sphincter
anteriorly and towards the patient's left.
And again on this image,
the tearing the internal sphincter is from 12 o'clock here
to approximately three o'clock here.

Here's another example.
Now I can tell I'm up relatively high here
because I can identify posteriorly that u-shaped sling
of the striated,
intermediate echogenicity of the,
pubal rec callus muscle
and notice that the external sphincter is going
to be closely opposed to that posteriorly.
But remember in this location you can't really
normally see the external sphincter anteriorly.
So I won't say that there's a external sphincter tear on
this image, but notice that there is a very large tear,
in the, in internal sphincter
and anteriorly between approximately the 10 o'clock
and the three o'clock position.

Sometimes having the patient clench can make things a little
bit more visible and we've pulled down a little bit.
So now I can clearly see the external sphincter.
And here once again, I can see
that tear in the internal sphincter from about 10 o'clock
to the three o'clock position.
And notice that I can now identify this hypo coic tear
disrupting the normal,
right echogenicity
of the external sphincter from 12 o'clock
to the three o'clock position.

Very often, as I have just shown you the tears are
what I would call,
congruent
and they're in the same location
and they're roughly the same size when you can compare the
tear in the external in the internal sphincter.
But this is not always so,
and again, it is very important to make sure
that the referring clinician knows whether
or not the tears are in the same location.
And if there's the same size.

So here in this patient you can see
that there's a big tear in the external sphincter from
approximately the nine o'clock
to the three o'clock position,
but there's only a very small anterior tear from in the
internal sphincter as you see here from approximately the 12
o'clock to the one o'clock position.

And here's another example.
Actually these are two different patients where again,
anteriorly, you see this very large hypo coic tear here in
the patient on the left from approximately 10 o'clock
to three o'clock, and the patient on the right from nine
o'clock to three o'clock in the an
external sphincter anteriorly.
But you have a very small tear from 12
to one in the patient on the left in the internal sphincter
anteriorly, and from maybe 11 o'clock
to one o'clock anteriorly in the internal sphincter,
you see this,
echogenic tear disrupting the hypo coic
rim of the ring
of the internal sphincter in the patient on the right.

So again, some discordance in the size,
although both of the tears are anterior.
And here,
is a different situation which again very important to,
identify for the referring clinician.
This patient clearly has a large tear in the external
sphincter and it goes from approximately 10 o'clock
to the two o'clock position.
You can see this big hypo coic,
heterogeneous tear disrupting the,
echogenicity
of the external sphincter.
But notice that the internal sphincter, this,
very,
very hypo coic ring is completely intact.
So here you have a tear of the external sphincter,
but an intact internal a**l sphincter.

And here's another example where again, the hypo coic ring
of the internal sphincter is completely intact,
but there is a large hypo
coer anteriorly from approximately 10 o'clock
to two o'clock in the external a**l sphincter.

And yet one more case showing a more,
intermediate echogenicity tear from about 11
to one o'clock in the external sphincter in the setting
of an intact,
hypo coic,
ring
of the internal a**l sphincter.

And this is kind of an unusual case
because this is a very small tear in the external sphincter.
Again, note that the inner hypo caulk ring of the
internal AAL sphincter is completely intact,
but there's a very tiny hypo coic tear in the external
sphincter from about the two o'clock
to the three o'clock position.
And this is,
somewhat unusual just
because the tear is so small.

Now, in this particular patient,
what you can see here on the left is
that both sphincters are intact,
but notice that there is variability in the width
of the internal sphincter and it is quite attenuated between
and thinned between the 12 o'clock
and the three o'clock position.
The patient on the right has a tear in the external
sphincter anteriorly.
As you see here,
relatively heterogeneous
hypo coic disruption of the external sphincter.
The internal sphincter is intact,
but notice again it is very thinned in kind
of an unusual location from about the three o'clock
to the six o'clock position.
And in addition, there seems to be compensatory hypertrophy
of the rest of the,
internal a**l sphincter,
which is thicker than what you normally see.

This patient has a tear anteriorly a large tear from about
the nine o'clock to the three o'clock position
of both the internal and the external sphincter.
And notice that the external sphincter is very
attenuated as well.
So again, it's important to pay some attention to the width
of the speak of the sphincters, how well you see them
because in this case surgery may not be all that helpful
because you can fix the tear,
but you're not gonna be able
to do much about the diffuse attenuation
of the external a**l sphincter.

And here is another patient that has somewhat complex,
problems and you can see an anterior in this patient on the
left you can see a tear anteriorly,
from about 10
to two o'clock in the external sphincter.
You can see that there's probably a tear from about nine
o'clock to two o'clock in the internal sphincter,
though perhaps there is a strand
or two of the internal sphincter present,
but it's at least extremely attenuated in that region.
But there's clearly marked hypertrophy
of the internal sphincter posteriorly.
And here you can see similar findings in another patient
with marked posterior hypertrophy of the internal sphincter
where it measures nearly six millimeters in diameter.
As I mentioned, four millimeters is usually the upper
limits, and again, a large tear here
of the external sphincter anteriorly
and marked either attenuation,
of the
and thinning of the internal sphincter anteriorly,
which I believe is still,
intact.
But really they're just a very few fibers
that are intact in the internal sphincter anteriorly.

Perianal Abscess and Fistula

Well, moving on to discussing perianal abscess and fistula.
In most patients,
these are due to obstruction
of the sphincteric glands, usually secondary
to fecal impaction.
But you can also,
develop perianal abscess fistula in the setting
of bowel inflammatory bowel disease, particularly patients
with Crohn's disease or patients who have other types
of infection and sometimes following trauma, again,
including rectal or a**l surgery.

And basically what the surgeon wants
to know here is the location of the fluid collections,
their size, and whether or not there are sinus tracts.
And if there are sinus tracts
or fistula, they need to know the relationship of these
to the sphincter, the number and the complexity.
And this is very, very important
because when they go into drain or resect these abscesses
or fistulas or sinus tracts, it is missing a sinus tract
that is the most common cause of recurrence
of this type of pathology.

So here is a example of a,
kind of lobulated,
very large peri rectal fluid collection
that is a perianal abscess.
And again, it's important to let them know how deep it goes.
And if you can't see how deep it goes with ultrasound,
further imaging with Mr
or possibly CT would be indicated.

We always look with color doppler
and it's a little bit surprising
that we didn't see any increased vascularity
in the peri abscess soft tissues,
but of course you would not expect
to see any vascularity within this conglomerate
appearing abscess.
If you did, you'd be concerned more that you had an abscess
or an underlying mass rather than a straightforward abscess.

These are some examples from the,
literature demonstrating in both cases very large horseshoe
or u-shaped abscess posterior to the anus
and posterior to the sphincteric complex, which
although immediately juxtaposed
to the abscess is not affected by it.
The patient on the left has a relatively homogeneous
fluid collection of intermediate echogenicity on the right,
the collection is a little bit more complex
and these little echogenic areas, of course
represent air within it.
Now this air could be from gas forming organisms,
but when you see air within the abscess,
it should make you question whether
or not there's fistulas connection either to the outside
or to the vagina or to the rectum.

Sometimes you can identify air,
within a fistulas tract,
looking through the vagina,
aiming your probe posteriorly.
And that was what was done here.
And here you can see the hypo coic internal a**l sphincter.
The more central echogenic bit here is the rectal mucosa.
And here anteriorly you see this focal echogenic area
that's got some dirty shadowing here.
And this represents air
that's disrupting the internal a**l sphincter anteriorly at
the 12 o'clock position.
And this was due to a vaginal a**l fistula.

Here is another example of a patient
with a vaginal rectal fistula,
and you can see this linear echogenic line on the trans
rectal ultrasound extending anteriorly from the vagina
through the external sphincter right up
to the internal sphincter,
although it doesn't involve the internal sphincter,
but you'll see some additional pathology,
namely from about the 10 o'clock to the 12 o'clock position
that there is a disruption of the internal sphincter.
So there's a tear of the internal sphincter in addition
to this fistula track to between the,
vagina
and the rectum or the anus.

And for those of you with really sharp eyes, you'll see
where the orange arrows are that there is a second
and perhaps a third echogenic linear tract
through the external sphincter to the level
of the internal sphincter at about the 10 o'clock position.
So this is a complex,
constellation of findings.
It's important that the surgeon know
that there is an accompanying tear of the internal sphincter
so that that can be fixed at the same time
that the fistulas tracks are resected
and that this isn't just a simple fistula through the
external sphincter at the one o'clock position,
but there there's a second
and possibly a third smaller tract at about
the 10 o'clock position.
And this is very important
because if one had missed these
tracks over here at the 10 o'clock position, as I mentioned,
this is a common cause for recurrence of
symptoms and even recurrent abscess formation.

And here is a final example
where you can see this echogenic material.
In this case it is in the interra sphincteric space
and involves the internal sphincter,
although the external sphincter does not appear to be,
so involved though again, we're up relatively high,
you're beginning to see some
of the pubal rec,
sling here.
So again, this is an example of air
disrupting the internal sphincter in the interra sphincteric
space at about the 10 o'clock position.

Staging Rectal Cancer with Ultrasound

Well, the last application of trans rectal ultrasound
that I wanted to discuss is its potential
for staging patients with rectal cancer.
And the beauty of trans rectal ultrasound is
that you can identify the different layers
of the rectal wall.
And this is the typical,
gut wall signature
that you can see with ultrasound.
And the layer that you really want
to carefully identify is this outer hypoechoic band,
which is a muscularis propria.
And the reason for that is, is
that if the tumor is contained
by this band is either in other words, central
and doesn't extend beyond that, it is a T two team or
and a T two tumor.
It can be treated with primary surgery.
If however, the tumor extends through the hypo coic
muscularis propria into the surrounding echogenic
adventitial layer or peri rectal fat,
it becomes a T three tumor.
And those tumors are optimally treated
with primary chemotherapy and radiation therapy
and only subsequently have surgical resection.

So here is an example of a very large rectal cancer.
This is the probe here,
and you can see all
of this hypo coic mass from about the 12 o'clock going
to the right and posteriorly
to the three o'clock position is all tumor.
You can see a little bit of the
rectal wall signature from anteriorly
and to the left,
here from the one o'clock
to the three o'clock position.
And there you can clearly identify the outer hypo coic rim
of the muscularis propria
and you can see that that rim is intact.
And the tumor, although very large,
is contained within that.
And this would be, although a very large tumor would be at
least by ultrasound a T two tumor, understanding
that ultrasound is not very good at differentiating
between microscopic invasion, the adventitia
and little inflammatory changes.

So really we typically only call T three tumors
or invasion of the adventitia when you see things like this
where you actually clearly can see lobular extensions
of the tumor clearly beyond the rim
of the hypo coic band of the muscularis propria.

So in these two patients, this is one patient down below
and a second patient anteriorly.
You can clearly see this large tumor disrupting all layers
of the rectal wall,
clearly extending anteriorly into the echogenic
per rectal fat.
And here in this very large tumor, you can see several areas
here at about four o'clock here from nine o'clock
to six o'clock, where you see these lobular extensions
of tumor into the peri rectal fat
and probably some adjacent lymph nodes as well.
So again, a T three tumor.

Conclusion

So in conclusion, transrectal ultrasound is easy.
It's safe, it's well tolerated, but it is operated dependent
and you need to know the anatomy in order
to interpret your images.
I think it ought to be the first line imaging modality
of choice for evaluation of a**l sphincter anatomy.
And it is extremely accurate in differentiating a true tear
from neurogenic,
injury.
And trans recal ultrasound in our experience has about a
hundred percent sensitivity
and a little bit less lower positive predictive value
for identifying these tears and determining whether
or not the external or internal sphincter
or both are involved.
And again, if these sphincters are intact, the cause
of the incontinence would be neurogenic injury.

I do want to advise you to recognize though
that sphincteric tears, particularly in the setting
of obstetrical trauma, do not very often occur in isolation.
And often they are involved with,
multicom compar disease,
with prolapse
and urinary incontinence.
And so sometimes Mr
or three-dimensional ultrasound of the pelvis can be helpful
to evaluate for posterior
or multi compartment,
disorders.

We used to do endo vaginal ultrasound in,
our practice
and have seen in the literature that it's reported
to have a hundred percent sensitivity
for at least internal a**l sphincter tears.
But we have actually had several false positives
and we certainly do not think it is very helpful
for evaluating tears of the external a**l sphincter.
So we no longer include,
endo vaginal ultrasound
for evaluation of the,
internal external sphincter in our practice.

And as always, one of the exciting parts about ultrasound
or some of the new technologies and advances
and in the future, I think three dimensional ultrasound
of the pelvis and
of the a**l sphincter will provide us even more information
to help our surgical colleagues.
Thank you very much.